1) Field of the Invention
The present invention relates to adhesive tapes for electronic parts to be used for adhering between parts around leadframes making up a semiconductor device, e.g., lead pins, semiconductor chip mounted substrates, radiation plates, semiconductors themselves.
2) Description of the Related Art
Conventionally, adhesive tapes for fixing a leadframe, TAB tapes, etc., are-used as adhesive tapes for use in the interior of resin-molded type semiconductor devices. For example, the adhesive tapes for fixing a leadframe have been used to fix lead pins of the leadframe in order to enhance the efficiency for producing the leadframe itself and the whole semiconductor assembly stages. In general, a leadframe manufacturer tapes a leadframe, and brings it to a semiconductor manufacturer, at which a chip is mounted thereon followed by molding the leadframe with a resin. For this reason, it has been required for the adhesive tapes for fixing the leadframe not only to possess general reliability in a level required for semiconductor and enough processability at the time of taping, but also to possess sufficient adhesive strengh immediately after taping and heat resistance enough for withstanding thermal process at the stages of assembling semiconductor devices. Conventionally, the adhesive tapes for use in such an application include adhesive tapes applying on a support film of a polyimide film, etc., an adhesive comprising a synthetic rubber resin such as polyacrylonitrile, polyacrylate or acrylonitrile-butadiene copolymer solely, or modified with any other resin or blended with any other resin to come into a B-stage.
In recent years, resin-molded type semiconductor devices as shown in FIGS. 1 to 3 have been developed or produced. In FIG. 1, the device has a construction in which lead pins 3 and plane 2 are connected by means of an adhesive layer 6, a semiconductor chip 1 is mounted on the plane 2, and together with bonding wires 4 between the semiconductor chip 1 and the lead pins 3, they are molded with a resin 5. In FIG. 2, the device has a construction in which the lead pins 3 on the leadframe are molded with the semiconductor chip 1 and an adhesive layer 6 and together with a bonding wire 4, they are molded with a resin 5. In FIG. 3, the device has a construction in which a semiconductor chip 1 is mounted on a die pad, electrode 8 is fixed with an adhesive layer 6, the spaces between semiconductor chip 1 and an electrode 8 and between the electrode 8 and lead pins 3 are each connected with bonding wires 4, and they are molded with a resin 5.
In the adhesive layer in the resin-molded type semiconductor devices shown in FIGS. 1 to 3, the use of an adhesive tape to which a conventional adhesive is applied has the problems such as insufficient heat resistance. Also, in the case of the application of polyimide resin, conditions of temperature and pressure for taping and conditions for curing are severe so that the metal material, such as leadframe, are damaged. Consequently, it has been desired to develop an adhesive for electronic parts which can be coated and cured at a relatively low temperature, and which has sufficient heat resistance and reliability, etc.
The present inventors have proposed an adhesive tape using an ahdesive comprising a piperazinylethylaminocarbonyl-containing butadiene-acrylonitrile copolymer represented by the under-mentioned formula (I) and a compound having at least 2 maleimide groups (Japanese Patent Application Laid-Open 126591/1995), whereby the above problems are dissolved.
However, there are still problems in this adhesive tape. Incase of using an adhesive tape comprising an adhesive layer on a heat resistant film, there are problems that the heat resistant film is delaminated from the adhesive layer at their interface because of insufficient affinity between the heat resistant film and the adhesive layer, and delamination is easily caused between the interface between the heat resistant film and the adhesive layer or between the adhesive layer and the substance to be adhered such as metal plane, etc., because they have each a different thermal expansion coefficient. Also, in case of using an adhesive tape composed of an adhesive monolayer, there is the problem, when adhesion is carried out with heat under pressure, that pointed ends of the leadframe are embeded in and went through the adhesive layer to contact with the surface of the substance to be adhered, by which reliability of the semi-conductor devices fall for lack of the electric insulation. In order to avoid such problems, when the adhesive layer is cured so as to inhibit contact of the pointed ends of the leadframe with the surface of the substance to be adhered, temporary adhesion of the adhesive tape to the substance to be adhered is difficult to carry out.